Patent GB-930848-A (GB)
Title: Improvements in or relating to cathode ray tube display apparatus
Inventor: PARKER ERIC
IPC: H04N5/65
Filed: 1960-11-02
Abstract: 930,848. Television. DECCA Ltd. Jan. 29, 1962 [Nov. 2, 1960], No. 37707/60. Class 40 (3). [Also in Group XL (c)] Reflections of ambient light by the screen of a cathode-ray tube (e.g. for television or radar display) are prevented from reaching the viewer by means of an optical filter 15 (Figs. 1 to 3) or 33 (Fig. 4) positioned, in front of the tube screen, within a hood 12, 13, 14 (Figs. 1 to 3) or 32 (Fig. 4) the arrangement being such that ambient light reflected by the filter is obscured by the hood. The filters are either neutral density filters or are tinted to attenuate ambient light more than light emitted by the tube screen. The filter 15, which is formed as a cylindrically curved sheet, is hinged at 16 and when not in use may be held against the top surface 12 of the hood by a spring clip 17. When this filter is also to act as an implosion guard (e.g. by forming it of thick material) the hinge is omitted and it is secured rigidly in the hood and to allow insertion of the hand behind the filter (e.g. for writing on the tube screen) a hinged or sliding door 18 is provided in the bottom surface 13 of the hood. The interior of the latter should be absolutely black but when this is not so reflections by the filter which are directed towards the top surface 12 of the hood are prevented from reaching an observer by providing the latter surface with a number of ribs 19. In the embodiment of Fig. 4 the filter 33, which comprises a thin sheet 34 of filter material supported on a rigid plate 35 of glass of polymethyl methacrylate resin, is arranged in a plane at 45 degrees to the plane of the tube screen and to enable visual data to be superimposed of the tube display the top surface of the hood 32 is provided with an aperture 45 above which is positioned a transparent glass or plastic plate 36 edge illuminated by lamps 37 so that data written on the plate appears as a virtual image. The plate 36 may be provided with a graticule (e.g. for range and bearing in the case of a radar display) or it may be made rotatable and carry bearing markers. Additional data (e.g. from a chart or map) may be superimposed on the display by means of an assembly 38 pivotally mounted at 49 (to allow access to plate 36) containing the chart or map 39 mounted on rollers 40 and including lamps 42 which form an image of the chart &c. (preferably consisting of translucent markings on an opaque ground) on the filter 33. A colour filter may be positioned below plate 36 if the additional data is required to be produced in a particular colour and to eliminate parallax effects due to the curvature of the tube screen a correcting lens may be positioned in the aperture 45. Other display devices e.g. meters or indicators may be positioned within the hood so that additional visual images are superimposed on the main display (or near the edge thereof) and where (e.g. in radar operations rooms) the user of the display requires to see also information such as carried on display boards on the walls of the room a mirror may be arranged above an aperture formed in the top of the hood such that the mirror and the filter 33 form a periscope.